1. Field of the Invention
The present invention relates to an impact detection system using an optical fiber sensor.
2. Description of Related Art
In a field in which both the strength and the weight saving of a material of, for example, the airframe of an airplane are required, it is indispensable to widely apply a composite material such as a carbon fiber reinforced plastic (CFRP) in order to meet the requirement of this kind.
As an apparatus for performing the detection of damage, a defect, and the like, of such a composite material, Japanese Patent Application Laid-Open Publication No. 2005-98921 describes a damage detecting apparatus using a fiber Bragg grating (FBG) optical fiber sensor. The thinning of the diameter of an optical fiber has advanced recently (for example, to be a diameter of 52 μm), and, if the optical fibers are embedded in a structure, the lowering of the strength of the structure is scarcely produced. Consequently, the optical fiber has the advantage that the degree of freedom of the installation thereof is high.
The invention described in the Japanese Patent Application Laid-Open Publication No. 2005-98921 detects the damage of a composite material on the basis of a change of the output of characteristic detecting means by vibrating the composite material with a piezo-element. The invention uses the following components for the detection of the damage: the piezo-element fixed to be disposed at a predetermined position of a composite material structure; a lead wire to transmit a signal to the piezo-element; the optical fiber sensor fixedly disposed so that the composite material constituting the composite material structure is put between the optical fiber sensor and the piezo-element, which sensor has a grating portion reflecting a light of a predetermined wavelength on a core portion; a light source performing the radiation of a light to a core portion; and the characteristic detecting means for detecting the characteristics of the reflected light from the grating portion. Moreover, a spectrum analyzer or the like to detect the frequency characteristic of the reflected light from the grating portion is used as the characteristic detecting means.
However, the invention described in the Japanese Patent Application Laid-Open Publication No. 2005-98921 cannot specify the existence, the position, and the magnitude of an impact having an arbitrary magnitude when an object structure receives the impact at an arbitrary position on the structure because the invention aims to detect a damage and the piezo-element is accordingly disposed at a predetermined position. Because the vibration of a reflected light from the optical fiber sensor (grating portion) changes according to the magnitude of the impact and the distance from the impact (vibration source), the system loading a known vibration on the object structure by the piezo-element to detect the damage on the basis of the propagation result of the vibration cannot grasp all the changes from a change of a reflected light vibrating large to a change of a reflected light vibrating small, and cannot specify the existence, the position, and the magnitude of an arbitrary impact with high accuracy.